Self-propelled working platforms or trucks such as a hydraulic shovel do generally have attachments connected to the ends of working arms of said platforms. An example of these attachments is a crushing apparatus, which will typically comprise a pair of end arms. Each of the end arms may be shaped as an array of fingers or crab's nails, and a hydraulic cylinder will operate to close or open the end arms.
When a building is demolished using such a crushing apparatus, an operator will have to control its position, posture and/or angular direction in which the pair of end arms are closed or opened, suitably for target article. In order to enable such an operation, those end arms need to swivel as a whole.
For the purpose of turning or swiveling each pair of end arms on the crushing apparatus, they may either be forced to swivel against a braking member to which they are pressed, or be driven automatically by an actuator such as an hydraulic cylinder.
In the former case of forcible swiveling, a crushing apparatus as disclosed in the Japanese Patent Publication No. 7-103700 may for example be used.
A body frame of the crushing apparatus shown in this publication '700 is connected by a swivel bearing to the arm of a power shovel or the like. A disc brake is employed in this case to impart a frictional resistance to the body frame of such crushing apparatus.
Crushing apparatuses of this type are simple in structure, and also advantageous in that any excessively strong torsion acting on each crushing apparatus during its demolishing operation would automatically cause it to rotate in such a manner as protecting it from breakage.
However, it is a disadvantage of this type crushing apparatuses that only those who are highly skilled are allowed to operate them.
Further, a fastening torque for the disc brakes incorporated in such prior art apparatuses is difficult to adjust easily and adequately. Any unintentional rotation resulting from contact with any obstacle or any offset in gravitational center of the crushing apparatus may advantageously be avoided, by selecting a stronger fastening torque for the disc brake. If the torque applied to the disc brake is too intensive, then an excessively strong impact will be needed to swivel the apparatus, thereby incurring an undesirable shock on it and causing its serious damage. A lower fastening torque may be adopted to resolve this problem. However, there will arise another problem that even any weak impact acting on the pair of end arms would be enough to unintentionally rotate them to a wrong angular position, thus lowering efficiency of breaking operations. A friction plate in each disc brake is likely to become worn out soon, impairing its braking effect. The friction plate should be replaced frequently with a new one, so that maintenance works including the adjusting of fastening torque have to be repeated many times.
A proper braking force will be maintained, only if such intricate adjusting and maintenance works are done by well-experienced and highly-skilled operators at considerably short intervals of time.
In the latter case of automatic swiveling, a hydraulic motor or the like has to be installed in the crushing apparatus so that a body frame thereof is operatively connected to said motor.
Discrete hydraulic fluid lines are necessary along the working arm of a hydraulic power shovel, respectively for the hydraulic cylinder for closing and opening the end arms and for the hydraulic motor for swiveling these arms. Distal ends of the two hydraulic fluid lines are adjoined to a hydraulic connector disposed on a bracket of the crushing apparatus, so that an operator within a cabin will use a pedal and/or lever to close or open the end arms and also to swivel same. Thus, the operator can do his work for swiveling the arms more easily by virtue of such a hydraulic system, although a complicated piping and a lot of hydraulic devices are indispensable.
It does not suffice to equip the hydraulic shovel with an oil piping for closing or opening the pair of end arms as the principal parts of a crushing apparatus attached to said shovel. Another piping independent of the said one piping and comprising a control valve, a maneuverable pedal and/or lever should be mounted on the prior art crushing apparatus in order to actuate the hydraulic motor for swiveling the pair of end arms. Thus, two independent oil lines necessary for the closing/opening and swiveling of the pair of end arms will raise material and labor costs in transforming the power shovel. In a case wherein an additional casing drain must be returned to a central reservoir for certain types of hydraulic motors, the material and labor costs will rise further.